RECIFE, BRAZIL - JANUARY 29: Dr. Valeria Barros treats a 6-week old baby born with microcephaly at the Lessa de Andrade polyclinic during a physical therapy session on January 29, 2016 in Recife, Pernambuco state, Brazil. Health officials believe as many as 100,000 people have been exposed to the Zika virus in Recife, although most never develop symptoms. In the last four months, authorities have recorded around 4,000 cases in Brazil in which the mosquito-borne Zika virus may have led to microcephaly in infants. The ailment results in an abnormally small head in newborns and is associated with various disorders including decreased brain development. According to the World Health Organization (WHO), the Zika virus outbreak is likely to spread throughout nearly all the Americas. (Photo by Mario Tama/Getty Images)
(2016 Getty Images)

GENEVA (AP) – The World Health Organization has begun a crisis meeting considering whether the explosive spread of the mosquito-borne Zika virus — which is linked to birth defects in the Americas — should be declared a global health emergency.

WHO spokesman Christian Lindmeier says the teleconference meeting of experts will consider whether international efforts to fight the outbreak should be immediately ramped up.

WHO last declared an emergency over the 2014 Ebola outbreak.

Last Thursday, WHO director-general Dr. Margaret Chan said the level of alarm was "extremely high" despite the lack of proof that Zika is responsible for the spike in the number of babies born in Brazil with abnormally small heads.

WHO estimates the Americas could see up to 4 million Zika cases over the next year.